Vulcanization of rubber



Patented Aug. 1945 I UNITED -STATES PATENT OFF-ICE VULCANIZATION OFRUBBER Philip '1. Paul, Naugatuck, Conn., assignor to United StatesRubber Company, New York, N. Y.', a corporation of New Jersey NoDrawing. Application August 31, 1944, Serial No. 552,206

Claims.

. This invention relates to the rulcanlzation of rubber and similarsulfur-vulcanizable rubberlike materials, by an improved processemploying a new accelerator mix. a

In the past, various organic accelerators containing at least one of theelements, nitrogen or sulfur, in chemical combination, have been used.

Frequently, their use, particularly of the nitrogencontainingaccelerators, has been attended by incipient vulcanization, known asburning or scorching.

I have foundpthat certain aryl sulfenamides, which ordinarily alone haveno substantial accelerating power, particularly in carbon blackstocks-nevertheless will retard the action of the cleus of the benzene,or naphthalene series, hav-' ing a nuclear carbon atom directly attachedto the S (sulfur), and which nucleus is further substituted by anelectro-negative group, e. g., halogen, nitro, acyl, carboxyl (-COOH)carboxy ester, sulfonamide, carbonyl amido, cyano (--CN) nitro alkylene,etc. Exemplary of acyl is such as CHaCO-; of carboxy ester, such as-COO.CH:; of sulfonamide, such as SO2.NH:; of'carbonyl amido, such asCO.NH2; of nitro allrylene, such as CH2.NO2. The electrd-negative groupalso operates to stabilize the chemical, which in turn allows processingwith a reduction in the danger of decomposition of the chemical, beforethe vulcanization. 4

Exemplary of preferred sulfenamides are:

o-Cyano phenyl sulfenamide o-Nitro phenyl sulfenamide m-Nitro phenylsulfenamide p-Nitro phenyl sulfenamide o-Fluoro phenyl sulfenamidem-Fluoro phenyl sulfenamlde' p-Fluoro phenyl sulfenamlde2,5-dichlorop1ienyl sulienamide 2,3,5-trichloro phenyl suli'enamidel-nitro naphthalene 2-sulienamide 2-nitro naphthalene l-sulfenamide1,4-dichloro naphthalene z-sulfenamide o-Carboxy phenyl sulfenamidep-Acetyl phenyl sulfenamide p-Ethyl carboxy phenyl sulfenamide .p-Chloroo-acetyl phenyl sulfenamide Z-methyl 4-n itro phenyl sulfenamide2-phenyl 4-nitro phenyl sulfenamide 4-ter.butyl 2-nitro phenylsulfenamide o-Sulfonamido phenyl sulfenamide 1 Among the usefulnitrogen-containingaccelerators, employable with any ofwhe abovesulfenamides, are the following:

Acetaldehyde-aniline condensation productsAcetaldehyde-butyraldehyde-aniline productAcetaldehyde-formaldehyde-aniline productAcetaldehyde-p-toluidine-aniline product Alpha-ethyl beta-propylacrolein-aniline product Tributylidene anilineButyraldehyde-monobutylamine product Formaldehyde-aniline productFoi'maldehyde-monoethyl amine product Formaldehyde-para toluidineproduct Diphenyl guanidine Di ortho tolyl guanidine Triphenyl guanidine2-mercapto thiazole 4,5-dimethyl Z-mercaptc thiazole *i-ethyl 2-mercaptothiazole 2-mercapto benzothiazole 2,2'-b enzothiazole disulfide Zinc2-benzothiazole sulfide Dinitrophenyl 2'-benzothiazole sulfide Phenylamino methyl 2-benzothiazyl sulfide- Bis-N,N' (2-benzothiazylthiomethyl) urea Benzoyl 2-benzothiazyl sulfide Benzothiazyl2-monocyclohexyl sulfenamide 2-mercapto thiazoline 2-mercapto 4-methylthiazoline Tetramethyl thiuram monosulfide Tetramethyl thiuram disulfideZinc dimetliyl dithiocarbamate Tetra ethyl thiuram. disulfide Leaddimethyl dithiocarbamate The use of these materials as delayed actionactivators for the primary vulcanization accelerators in addition toimparting a more favorable scorch factor also allows greater freedom ofcompounding variation. By varying the ratios of accelerator andactivator it is possible to obtain a series of combinations whichvary.in scorch and curing properties. Indeed, in some cases it may be founddesirable to use a preponderanc of the activator so as to have a rubberstock that is ex- Scorch tests 120 minutes at 5 pounds tremely safe andyet not too highly cured. Conseper square inch steam pressure quently,the ratio of activator to accelerator is to be chosen, dependent on thetype of rubber (nat- A B c D E ural or synthetic), type of stock (whitestock, 5 F tread stock, etc.), temperature of cure, time of T E T E T ET E T E cure, the particular primary accelerator, for example, in thecase of mercapto benzothiazole 1,607 612 240 805 902 632 73s 15s to1,070 No cure. (Captax) the proportion of activator generally rangesfrom 25 to 200% by weight, based on the T means tensile strength inpounds persquareinch. weight of the Captax, and lastly the objectives ofEmmaI 2 the compounder, i. e., whether he desires to provide a low orhigh modulus stock, to provide for Master batch-B a short or a longcure, etc. p l crepe 00 For the tests given below, the ortho and para,Zinc oxide 0 nitro phenyl sulfenamides may be prepared by whiting 60 theaction of anhydrous ammonia. on the corre- Lithopone 60 spondingnitrophenyl sulfur chloride according to z lam-ate 05 the method ofZinck & Farr, Annalen 391, 57-88 Sulfur 3 (1912). The 4-chloro2-nitrophenyl sulfenamide g0 (M. P. 126-127 C.) may be preparedaccording to 2335 the method of Zinckeet al., Annalen 416, 86-112 7(1918). G H I I K L The 2,4-dinitrophenyl suli'enamide (M. P. 119- 120C.) may be prepared from 2,4-din1tro thiophenol and monochloramine inthe w t solup ififiiifiii iig iaifiifiatiiij ff.. fif ffu ff tion; thesereagents react at 0 C. to form the vm hen lsuli r r id 0.35 0.3a 0.35said sulfenamide which can be filtered of! and i g fififii' 11m; c 1.0 5washed with water. '2mercapto thiazoline I 1.0 0.7

The 2,5-dichlorophenyl sulfenamide (M. P. 61-

' Cured 30 minutes at 30 pounds per square inch steam pressure rams a. K

3 400 m sea :70 m no mo 1,230 1,225 1,150 um 000 1.000 Break 2,530-6562.2110410 2,200-655 asao-m moo-ow awn-07o 62 C.) may be prepared from2,5-dichloro thio- Scorch tests 75 minutes at5 pounds phenol andmonochloramine, in the same manner per square inch steam pressure as thepreceding chemical. a

The following examples, in which the partsare by weight, ar given toillustrate the invention: o H I J K L EXAIPLI 1 I a 'l n Mmefbat I A v00 T 1: E T E T E T Smoked Sheet 1 3 14; Carbon black 45 so w m 1. 0 244mi 1m 8w q Zinc laurate Pine tar Zinc oxide 5.0 3 SulfurAcetone-diphenylamine I condensate (antioxidant) M N 0 P 161-0Mmerbmh-B---.- 233.5 233.5 nu ma 'lhluole mixture 1.0 0. 5 o-Nitrohenylsnliemmldc... 0.35 0.36 E F Benny fl-benzothiuylmlflde 1.6 0.8

Thiazole mixture is a mixture of bis-4,5411- methyl fli'iazyl disulfldeand blsAli-dir B5 methyl thiazyl disulflde (15%). Cum! 415 minutes at 30pounds per squafe inch. steam-pressure A n 'o 1) a r 3w e20 610 8!) 710No cure.

000 1,000 1.1m 1,810 riiiiililiii to :3 3.0 0 000 aoso-m moo-00o moo-usCured 45 minutes at 30 pounds per square inch.

' steam pressure Percent elongation (E) M N Scorch tests 75 minutes atpounds per square inch steam pressure M N 0 P T E T E T n T- E EXAMPLE 4Q R S T Master batch-B 233.5 233.5 233.5 233.5 Tetramethyl thiurammonosulfide 0. 16 0.08 o-Nitrophenyl sulienamide 0.35 0.35Butyraldehyde-aniline condensate 0.5 0.25

Cured 45 minutes at 30 pounds per square inch steam pressure Cured 45minutes at 30 pounds per square inch steam pressure Per cent elongation(E) U V 875 330 $313: 2,100 2,030 Break 090-656 3, coo-cs0 Scorch tests105 minutes at 5 pounds per square inch steam pressure Exmud w Yz Cured60 minutes at-30 pounds per square inch steam pressurePeroenteionxationflf) W X Y- Z 2% 2 338 2 1 3.0004100 3.190 610 mad-6Scorch tests 1 05 minutes at 5 pounds per square inch steam pressure w xY, z I

T E T E T E T. E

Cured so minutes at so pounds per s uare inch 40 steam pressure PM:elongation in 1' B I 49o 1mm: I 3, 125 616 soz sss Scorch tests 105mum-8 at s poundsper s quare inch steam pressure It is to be understoodthat the terin a. rubber" is employed in the claims in a generic senseto refer to natural as well as synthetic rubbers which are capable ofvulcanization when heated with sulfur, and includes 'caoutchouc, balata,autta. percha, polybutadienes, and'modifled polybutadienes, such as GRSand GRN (respectively, butadiene-styrene copoiymer rubber, andbutediene-acrylo-nitrile copolymer rubber), as well I as latices andreclaims ot'such materials. whether or not admixed with pigments,fillers, softeners, antioxidants, etc. I

Other ratios of the compounding ingredients than those mentioned in theexamples given, as well as other wellknown fillers. Pi8ments, etc., maybe employed in the production of variws types 0! rubber compounds, andare apparent to those skilled in the art to which the invention prtains.

Having thus described my invention, what I claim and desire to protectby Letters Patent is:

1. A method of vulcanizing a rubber which 35 comprises incorporatingtherein sulfur, a primary organic rubber-vulcanization accelerator, anda compound having the general formula ArylSNH2 where aryl represents anaromatic nucleus of the group consisting of the benzene 4 andnaphthalene series, having a nuclear carbon atom directly bonded to theS, and which nucleus is further substituted by an electro-negativegroup.

2. A method of vulcanizing a rubber whic comprises incorporating thereinsulfur, a primary organi rubber-vulcanization nitrogencontainingaccelerator, and a compound having the general formula ArylS--NH2 wherearyl represents an aromatic nucleus of the group consisting of thebenzene and naphthalene series, having a nuclear carbon atom directlybonded to the S, which-nucleus .is further substituted by an,electro-neg'ative group, and heating the mix.

3. A method of vulcanizing a rubber which comprises incorporatingtherein sulfur, a primary organic rubber-vulcanization accelerator, andortho-nitrophenyl sulfenamide having the formula 4. A method ofvulcanizing a rubber which comprises incorporating therein sulfur; a-primary organic rubber-vulcanization; nitrogencontaining accelerator,and ortho-nitrophenyl sultenamide having the formula and heating themix;

5. A method of vulcanizing a rubber'wliich comprises incorporatingtherein sulfur, a primary organic, rubber-vulcanization accelerator, and2,5-dichloro phenyl sulfenamide having the formula 6. A rubberc0mp0sition containing a primary organic rubber-vulcanizationaccelerator, and a compound. having the general formula Aryl-S-NH: wherearyl represents an aromatic nucleus of the group consisting of thebenzene and naphthalene series, having a nuclear carbon atom directlybonded to the S, and which nucleus is further substituted by anelectro-negative group.

7. A rubber composition containing a pri-,

mary organic rubber-vulcanization nitrogen-containing accelerator, and acompound having the general formula ArylS-NH: where aryl repre',-

' sents an aromatic nucleus or the group consisting of the benzene andnaphthalene series, having a nuclear carbon atom directly bonded to theS,

which nucleus is further substituted by an electro-negative group, andheating the mix.

8. A rubber composition containing a primary organicrubber-vulcanization accelerator, and ortho-nitrophenyl sulfenamidehaving the formula '9. A rubber composition containing a primary organicrubber-vulcanization nitrogen-containing accelerator, andortho-nitrophenyl sulfenamide having the formula l and heating the 10. Arubber composition containing a primary organic rubber-vulcanizationaccelerator, and 2,5-dichloro phenyl sulfenamide having the formulaPHILIP T. PAUL.

